Control of the Mesoscopic Organization of Conjugated Thiophene Oligomers, Induced by Self-Assembly Properties

Abstract

Conjugated polymers and oligomers, derived from phenylene phenylenevinylene or thiophene, have been used as active semiconducting layer in various organic-based thin film devices, such as field-effect transistors, FET,^1–4 and light emitting diodes, LED.^{5, 6} These devices present a large potential interest on a fundamental point of vue, for the analysis of the mechanism of charge generation, transport and recombination in organic materials, and also for many envisionned applications in the field of electronics and optoelectronics. These organic semiconducting materials are formed by the assembly of molecules held together by weak van der Waal forces, which means that the properties of the solid are directly given by those of the individual molecules, and also by the way these molecules are spatially ordered in the material. These features open very attractive perspective for controlling the materials properties through the molecular engineering of these assemblies, and a tailoring of the electronic properties of organic molecular semiconductors can be expected through the modification of the chemical structure of their constituting molecules. In the literature, the chemical variation of polyparaphenylenevinylene has already been shown to allow the tuning of the band gap and emission wavelength of electroluminescent diodes based on these materials.^7–9 Similarly, we have shown that the increase of the conjugation length of well defined conjugated thiophene oligomers leads to a spectaculor increase of the charge transport properties, as expressed by the high carrier mobility observed in field-effect transitors based on sexithiophene.¹⁰